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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Part 4 (Details) (USD $) | 12 Months Ended
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Sep. 30, 2013 change | Sep. 30, 2012 | Sep. 30, 2011
Off System Sales [Line Items] |  |  |
Number of PGA Discretionary Changes | 3 |  |
Months between PGA Discretionary Changes | 2 months |  |
Cost savings retention percentage | 10.00% |  |
Maximum amount of cost savings allowable | $ 3,000,000.0 |  |
Number of Months of the Original Maturity of Debt Instruments Purchased | 3 months |  |
Gross Receipts taxes recorded in regulated gas distribution operating revenues | $ 40,800,000 | $ 35,900,000 | $ 43,500,000
Laclede Gas [Member] | First $2 million [Member] |  |  |
Off System Sales [Line Items] |  |  |
Customer Share | 100.00% |  |
Company Share | 0.00% |  |
Laclede Gas [Member] | Next $2 million [Member] |  |  |
Off System Sales [Line Items] |  |  |
Customer Share | 80.00% |  |
Company Share | 20.00% |  |
Laclede Gas [Member] | Next $2 million [Member] |  |  |
Off System Sales [Line Items] |  |  |
Customer Share | 75.00% |  |
Company Share | 25.00% |  |
Laclede Gas [Member] | Amounts exceeding $6 million [Member] |  |  |
Off System Sales [Line Items] |  |  |
Customer Share | 70.00% |  |
Company Share | 30.00% |  |
Missouri Gas Energy (MGE) [Member] | First $1.2 million [Member] |  |  |
Off System Sales [Line Items] |  |  |
Customer Share | 85.00% |  |
Company Share | 15.00% |  |
Missouri Gas Energy (MGE) [Member] | Next $1.2 million [Member] |  |  |
Off System Sales [Line Items] |  |  |
Customer Share | 80.00% |  |
Company Share | 20.00% |  |
Missouri Gas Energy (MGE) [Member] | Next $1.2 million [Member] |  |  |
Off System Sales [Line Items] |  |  |
Customer Share | 75.00% |  |
Company Share | 25.00% |  |
Missouri Gas Energy (MGE) [Member] | Amounts exceeding $3.6 million [Member] |  |  |
Off System Sales [Line Items] |  |  |
Customer Share | 70.00% |  |
Company Share | 30.00% |  |

X
- Definition The revenue of off system sales attributable to the entity. + References No definition available. + Details
Name: | lg_CompanyShare
Namespace Prefix: | lg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Percentage of savings due to cost management program allowed to be retained by the entity. + References No definition available. + Details
Name: | lg_CostSavingsRetentionPercentage
Namespace Prefix: | lg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The revenue of off system sales attributable to customers. + References No definition available. + Details
Name: | lg_CustomerShare
Namespace Prefix: | lg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount of gross receipts taxes associated with natural gas utility service, which are imposed on the Utility and billed to its customers. + References No definition available. + Details
Name: | lg_GrossReceiptsTaxAmountsIncludedOperatingRevenues
Namespace Prefix: | lg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Maximum amount of annual cost savings that the utility is able to retain under cost savings plan. + References No definition available. + Details
Name: | lg_MaximumAmountOfCostSavingsAllowable
Namespace Prefix: | lg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Minimum number of months that is required between discretionary PGA changes. + References No definition available. + Details
Name: | lg_MonthsbetweenPGADiscretionaryChanges
Namespace Prefix: | lg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of months the original maturity of debt instruments purchased can not exceed to be considered cash equivalents. + References No definition available. + Details
Name: | lg_NumberofMonthsoftheOriginalMaturityofDebtInstrumentsPurchased
Namespace Prefix: | lg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of discretionary PGA changes the Utility can make during each fiscal year. + References No definition available. + Details
Name: | lg_NumberofPGADiscretionaryChanges
Namespace Prefix: | lg_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | lg_OffSystemSalesLineItems
Namespace Prefix: | lg_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration